This research considers the effect of the extraceullar conducting space on propagation in the adjoining cardiac tissue through the use of electrophysiological/mathematical models and computer simulation. Expected effects include modification of velocity, waveform and safety factor. The quantitative effect is also expected to be different for longitudinal as contrasted with transverse propagation. Simulation will be performed on a multifiber slab and a multifibered cylinder lying in an extensive volume-conduction region. The simulation will be conducted using a bidomain tissuemodel and an Ebihara-Johnson membrane model initially. Following this, the inclusion of the recovery period as well as the effect of discrete junctions will be considered. Conditions to be evaluated include the effect of premature stimulii, and channel blocking drugs as well as variations in the physical size of the tissue, its conductivity parameters, and the membrane parameters.